Bio-fuels provide a viable route to aid in providing critical transportation energy needs in the US. They can also help in addressing global political instability evolving from reliance on foreign fuel. At present, most bio-fuels produced as ethanol are generated from corn starch. But this can meet only a small portion of US fuel requirements. Plant cellulose is an acceptable source of bio-energy, and its conversion for cellulosic bio-energy crops, which are both abundant and renewable, is a promising alternative approach.
Cost of effectively breaking down cellulose into fermentable sugars has been a major issue slowing cellulosic ethanol production. Many methods have been developed over the years to aid in the conversion of cellulose fibers into fermentable sugars. However, even with today's technology, conversion of lignocellulosic biomass of these crops into fermentable sugars for bio-fuels requires relatively expensive pretreatment processes that can also result in unwanted residuals that may interfere with the fermentation process.
A few of the methods applied in the pretreatment process include Dilute Acid, Flowthrough, Partial Flow, Controlled pH, AFEX, ARP, Supercritical CO2 Explosion, and Lime. In addition, these processes are either expensive, time consuming or both. Currently, pretreating cellulose with acid is a common way to break the material down into fermentable sugars. Most of these systems result in unwanted by-products from the process. The general perception is that these by-product compounds are detrimental and should be removed. Thus, after acid pretreatment, the resulting material is washed and detoxified. That can remove nutrients necessary for efficient fermentation. Washing, detoxifying and adding nutrients back into the pretreated cellulose are three separate steps with each step being expensive, adding to the already high cost of processing bio-fuel.
Claims for minimizing losses from by-product residuals have been made by proponents of the Ammonia Fiber Expansion (AFEX) explosion system with research indicating that chemical compounds that are created when the cellulose fibers go through the ammonia fiber process can improve the overall fermentation process. Developers claim that with this process the cellulose doesn't have to be washed or detoxified, allowing ethanol to be created from cellulose without added nutrients or other steps. Developers are working to improve the efficiency of the system in an attempt to lower its cost.